Conventionally, in the assembly of a bicycle frame, as illustrated in Taiwan Patent No. 584123, a bicycle frame of a bicycle, end portions of the transversal upper tube, lower tube, or rear bi-forked tube resist against and welded to a cambered surface of a longitudinal tube. Thereby the tubes are formed as a bicycle frame.
In above bicycle frame, the connection area is small so that the welding area cannot suffer from a heavy load. Thereby it is easy to have mechanical fatigue if the bicycle moves on uneven paths. Furthermore, the structure is destroyed.
In Taiwan Patent Publication with No. 527263, a manufacturing method for an aluminum frame with an integral formed multi-stub tubes is disclosed. The multi-stub tubes are used to increase the connection areas. However this prior art needs a multi-stub tube so that the many aluminum extrusion and cutting processes are necessary. Thus, the time is prolonged and cost is increased. Furthermore, this technology is particularly used to a specific structure, such as a front bi-forked tube. By a tube with at least two hollow areas, this induces many confinements and inconveniences.